Let the steak sit out on the counter for 30 minutes until it comes to room temperature.
Pat with paper towels then rub a generous amount of the steak spice on both sides.
Start your oven broiler with one oven rack at the top, and one oven rack in the middle.
Place the oil in the bottom of a cast iron or oven safe skillet and place on the top oven rack and heat up.
Once the oil is heated, place the steak into the hot skillet and sear on both sides for 2 minutes, or until browned as you like.
Once the steak is browned, reduce the oven heat to 300 °F and place the skillet on the middle oven rack. You can place the thyme sprigs on top and around if desired.
Cook for another 7-10 minutes until the steak reaches the desired temperature. Remove and place the porterhouse steak into a cutting board to rest for 5 minutes. The steak will rise another 5 degrees in temperature, so take that into consideration when removing from the oven.